Apparatus for relative gravity measurements



Aug. 4, 1942. G. A. vlslNcs 2,291,628

APPARATUS FORy RELATIVE GRAVITYMEASUREMENTS Filed Feb. 23, 1938 ,e/ i ll 1:/ y?? 16? Patented Aug. 4, 1942 APPARATUS FOR RELATIVE GRAVITYMEASUBEMENTS Gusta! Adolf Ising, Djursholm, Sweden Application February23, 1938, Serial No. 192,154 In Sweden February`24, 1937 (CL 26S-1.4)

1 Claim.

The present invention relates to apparatus for measuring gravity.

The usual method for relative measurements of gravity is based on theuse of an ordinary invariable pendulum, the period of swing of which ismeasured at diierent stations with as high accuracy as possible. Inmodern times, however, the pretensions of accuracy have become veryhigh, especially when exploring a small district for prospectingpurposes, for instance when searching for mineral or oil deposits, sothat the usual method requires a complicated, heavy and expensiveapparatus and rather long time of observation.- Therefore, other methodshave been employed which either do not require any time-observations atall or require only observations of moderate accuracy. In these priormethods a force proportional to the gravity acceleration and due to theweight of a certain movable mass is compared with another forceindependent of the gravity acceleration and as a rule of elastic originderived from a spring or an enclosed gas volume.

With these known methods two difculties arise in connection with theelastic force, namely its variation with the temperature and theso-called elastic after-Working.

An object of the present invention is to reduce materially both thediilculties mentioned, by choosing for the force of comparison anelectrostatic attraction or repulsion from at least one chargedconductor which is insulated and conveniently placed in an evacuatedvessel together with the movable mass. The electrostatic force iscompletely free from after-working and its dependency upon thetemperature will ybe comparatively small, when the force originates frominsulated electric charges, as this dependency is only indirectlyprovoked by the heat-dilatation of the bodies. By conveniently choosingthe material and arrangement of the conductors and insulators, theeffect of this heat dilatation may be compensated or at least renderedvery small.

'I'he evacuation reduces the conductivity of the gas, so that the chargeon the insulated conductor and thereby force of comparison will be keptvery nearly constant during a long time.

In carrying out the invention an instrument may be used which is basedon the same principle as an'electroscope. Before commencing thegravity-measurements at least one of the conductors of the instrument ischarged and then insulated. The instrument is then transported, whilekeeping its charge unchanged, to

the diierent observation stations where its indications are observed.

The invention will be more apparent upon a consideration of thefollowing detailed descrip- I tion and the accompanying drawing in whichtwo diii'erent embodiments are illustrated schematically.

Figure 1 is a vertical section of one embodiment; and

Figure 2 is a section on line 2-2 in Figure l.

With particular reference to Figure 1 there is provided an evacuatedvessel I. The vessel I contains an insulated metal plate l2 which is theconductor to be charged. 'I'he charged plate 'I2 attracts a pointer I3which is able to turn about a horizontal axis I 4, such as a stretchedhorizontal torsional wire, and carries a mirror I5. A screen IB providedwith a central slit delimits the electric eld and also, by means of theedges 30 of said slit, provides stops for preventing too greatdeviations of the pointer I3 from horizontal position. The pointer I3is, through the conducting wire I4, electrically connected with thecasing I and may, during the transports of the instrument, be keptarrest`e`d by means of some known clamping device.

For the purpose of charging of the plate I2 a stopper I1 of insulatingmaterial is arranged in a corresponding opening in the wall of thecasing, said stopper carrying a bent metal rod I8 which, by turning thestopper, may be brought into contact with an extension I 2 of the plateI2. The vessel I is evacuated through a stop cock I9. The opticalviewing system consists of a. Vertical telescope in which 20 is theobjective lens, 2| an eyepiece, 22 a scale and 23 a crosswire. The scaleand the crosswire are approximately in the focal plane of the objective,the scale conveniently being placed a little sideway from the opticalaxis or raised from the focal plane in Fig. 1 so that only its image inthe mirror I5 is visible through the eyepiece,- while the crosswire 23is directly viewed through the eyepiece. K

In operation of the apparatus and when the device is in one position orat a base station the plate I2 is charged momentarily by connecting theplate through the rod I8 to one terminal of a potential source such as abattery (not shown). The other terminal of the source is adapted to beconnected to the casing I. After disconnecting the plate I2 from thepotential source the position of the pointer I3 is observed by notingthe position of the mirror I5 through the telescope. 'I'he instrument insuch a charged condition may then be transported to some other point orstatiolwhere the gravity may be as= sumed to be greater than at the rstpoint or station of measurement. The pointer i3 will then assume adiierent position which will provide an indication in the difference ofgravity.

While the invention has been described with reference to specicstructural details it will be appreciated that changes may be madewithout departing from the spirit and scope oi the invention as setforth in the appended claim.

I claim:

A static gravimeter comprising in combination, a conductive pendulumsuspended in such manner as to be able to tum about a horizontal axis,

stops restricting the movement of said pendulum to small deflectionstrom a horizontal position. optical means for observing thedisplacements vof the pendulum. a stationary conductor disposed nearsaid pendulum, an evacuated receptacle hermeticaliy enclosing saidconductors, means highly insulating one of said conductors so as toenable it to retain a substantially invariable electrostatic charge theelectrostatic field oi' which constitutes substantially the wholecompensating force counter-balancing the weight of the pendulum so thatsuccessive observations at diierent places may be carried out withoutrecharging.

GUSTAF ADOLFl ISING.

